1. Field of the Invention
The present invention relates to a valve system for preventing effusion of fuel from the fuel tank and a valve device used therefor, more particularly to a device and a system for preventing the outflow of fuel from the fuel tank when a vehicle is accelerated, decelerated, makes a turn, ascends or descend a slope.
2. Description of the Prior Art
One of the conventional devices of this type is disclosed in the specification of U.S. Pat. No. 3,910,302, which is shown in FIG. 4. This device is provided in a fuel tank 30 so as to directly sense the change of the fuel level in the fuel tank which changes depending on the condition when a vehicle is accelerated, decelerated, makes a turn, ascends or descends a slope.
A cylindrical valve case 34 that forms a valve chamber 33, in which a cylindrical float valve 32 is fitted afloat, is joined to the end of a pipe 31 that communicates with a charcoal canister. A conical seat surface 36, to which a spherical seal 32 of the top end of the float valve 32 can be brought into contact, is provided on the top surface of the valve case 34. Several small holes, through which fuel flows into said case, are provided in the bottom surface or the side surface. Several ribs 35, which control the movement of the float valve 32 in the radial direction, are provided on the outer peripheral surface of the float valve 32.
When the liquid level in the fuel tank 30 changes at the time of acceleration, deceleration, climbing, descending or turning and fuel flows into the valve case 32, the float valve is subject to buoyancy and a spherical seal 32a at the top of the valve 32 comes into contact with seat the surface 34a of case 34 to prevent the fuel from flowing out of the tank.
In the conventional device mentioned above, the fuel that has flowed into the valve case subjects the float valve to buoyancy and prevents the fuel from flowing out of the tank. However, there is a possibility that the float valve does not contact the underside of the valve case under its own weight because of the action of surface tension of the fuel that has flowed out into the valve case even when the liquid level is stable and interruption of communication between the fuel tank and the charcoal canister is maintained. Such condition involves problems in that the evaporated fuel pressure in the fuel tank tends to rise so as to damage the seal of the fuel tank cap, or the evaporated fuel pressure in the fuel tank tends to be lowered due to the lowering of the liquid level as fuel is consumed, to deform the tank.